1. Field of the Invention
The invention relates to a power supply cord positioning device for a lighting unit, more particularly to a positioning device for securing a power supply cord inserted into a lighting unit, which ensures water-tightness and which can accommodate thermal expansion of a plastic shell of the lighting unit.
2. Description of the Related Art
With reference to FIGS. 1 and 2, a conventional lighting unit 1, such as a night lamp, is electrically connected to a power supply source via a power supply cord 11, and generally includes a plastic, light transmissive shell 12 and a power supply cord jacket 13. The shell 12 includes left and right shell halves 122, 121 which mate with each other to cooperatively confine a light bulb receiving chamber. One side of the shell 12 is provided with an outer mounting wall 123. An inner mounting wall 124 is disposed inwardly of and parallel to the outer mounting wall 123. The outer mounting wall 123 is formed with a transverse outer hole 125. The inner mounting wall 124 is formed with an inner hole 126 corresponding to the outer hole 125. The power supply cord jacket 13 is mounted in the outer and inner holes 125, 126, and includes a surrounding jacket wall 131 that defines a transverse cord hole 132 for passage of the power supply cord 11. The surrounding jacket wall 131 includes a clamped section 133 that is clamped between the outer and inner holes 125, 126, an enlarged inner positioning section 134 that extends from one end of the clamped section 133 toward the shell 12, and an enlarged outer positioning section 135 that extends from the other end of the clamped section 133 outwardly of the outer mounting wall 123 so as to abut against the latter. In other words, the clamped section 133 has a surrounding wall 136 with a width or diameter that is reduced with respect to the inner and outer positioning sections 134, 135.
In order to ensure water-tightness of the lighting unit 1, the surrounding wall 136 of the power supply cord jacket 13 is in tight fit with the inner and outer holes 126, 125 in the shell 12. Therefore, when the power supply cord jacket 13 is installed on the shell 12, the tight fit between the surrounding wall 136 and the inner and outer holes 126, 125 prevents entry of water vapor into the receiving chamber within the shell 12. Nonetheless, since the plastic shell 12 may expand or contract under temperature influences and may age with the passage of time, and under the circumstance that the power supply cord jacket 13 and the shell 12 are in tight fit, the shell 12 may easily crack, thereby affecting the water-tightness effect of the lighting unit 1. If dampness gains entry into the receiving chamber of the shell 12, corrosion and short circuit may occur. The service life of the lighting unit 1 may also be shortened.
Therefore, the object of the present invention is to provide a positioning device for securing a power supply cord inserted into a lighting unit, which ensures water-tightness and which can accommodate thermal expansion of a plastic shell of the lighting unit.
Accordingly, a positioning device of the present invention is adapted for securing a power supply cord inserted into a lighting unit which includes a light transmissive shell confining an accommodation chamber and having a lower inner peripheral edge portion which defines a lower opening to communicate with the accommodation chamber. A lighting source is disposed in the accommodation chamber and is electrically connected to the power supply cord. The positioning device includes a bottom wall with a periphery, a surrounding wall, a tubular insert member, and a bracing member. The surrounding wall extends from the periphery in an upright direction, and is adapted to be integrally formed with the lower inner peripheral edge portion of the shell to close the accommodation chamber water-tightly. The surrounding wall includes a mounting wall area which has outer and inner mounting wall surfaces opposite to each other in a first transverse direction transverse to the upright direction. The mounting wall area includes left and right lateral edge portions that are separated along a split line extending in the upright direction and that are in water-tight and detachable engagement with each other. The left and right lateral edge portions respectively include left and right abutment wall surfaces which face each other in a second transverse direction transverse to both the upright direction and the first transverse direction, and which extend respectively in the first transverse direction to interconnect the outer and inner mounting wall surfaces. The left and right abutment wall surfaces respectively have left and right cutout portions which cooperate to form an inner surrounding clamping wall surface that confines an insert hole. The insert hole is of a first dimension and extends in the first transverse direction to communicate the outer and inner mounting wall surfaces. The inner surrounding clamping wall surface has inner left and right clamping wall segments which respectively extend inwardly and in the second transverse direction from the left and right abutment wall surfaces. The insert member includes outer and inner tubular wall surfaces opposite to each other in radial directions. The inner tubular wall surface is adapted to wrap around and to bring the power supply cord into the lighting unit. The outer tubular wall surface includes: a surrounding neck segment which has front and rear surrounding end portions opposite to each other in the first transverse direction and which is disposed to be surrounded by, and spaced apart from the inner surrounding clamping wall surface by a surrounding clearance which is of such a dimension as to accommodate thermal expansion of the mounting wall area and to form, as a result of surface tension of an initial water vapor trapped therein, a moisture barrier against intrusion of water vapor; an enlarged surrounding head segment extending from the rear surrounding end portion in the first transverse direction and inwardly of the inner mounting wall surface so as to abut against the inner mounting wall surface; and a surrounding abutment segment extending from the front surrounding end portion in the first transverse direction and outwardly of the outer mounting wall surface so as to abut against the outer mounting wall surface. The bracing member is disposed between the inner surrounding clamping wall surface and the neck segment of the insert member.